This invention relates to a temperature control system for an internal combustion engine having a plurality of separate heat exchangers, one of which may be a coolant radiator, for cooling various fluids used in the engine.
Increased fuel efficiency is obtained in large internal combustion engines, such as those used in trucks, by providing additional heat exchangers in front of, or within, the normal engine coolant radiator in order to cool some of the fluids required to operate the engine, such as the lubricating oil and the turbocharged air when a turbocharger is employed. Optimum engine performance is obtained when the temperatures of those fluids, as well as that of the engine coolant, are established at desired levels. Air becomes hotter when it is compressed in a turbocharger. For maximum efficiency, however, the heat picked up in the compression process should be removed, to maintain the air's density, before the air is fed to the engine. Thus, it is common practice to run the pressurized air through an air cooler after it leaves the turbocharger and before it enters the engine.
A variable speed fan drive, controlled in response to the engine coolant temperature, is usually provided to blow through the coolant radiator, as well as through the other heat exchangers, the amount of air that is needed to maintain the coolant temperature at the level which will achieve optimum engine performance. Unfortunately, the fluids to be cooled by the various heat exchangers normally have different desired operating temperature ranges for best performance. As a consequence, when the amount of cooling air drawn in by the fan is determined by the engine coolant temperature, the temperatures of one or more of the other fluids may rise well above their desired operating ranges, the overall engine performance thereby suffering and becoming less efficient.
The present invention overcomes this shortcoming of prior engines having multiple heat exchangers and controls the fan drive in such a way that the fluids cooled by those heat exchangers never exceed their operating temperature ranges, thereby improving and optimizing the engine performance.